Sensor system for determining the control signals activating ciliary muscles

ABSTRACT

In a sensor system for determining the control signal supplied to the ciliary muscles of an eye for adjusting the focal length of the lens of an eye, a contact element of an electrically non-conductive material and provided with sensors is disposed on the cornea of the eye so that the sensors are arranged in contact with an annular area of the cornea next to the ciliary eye muscles so as to be able to sense the focal adjustment signals supplied to the ciliary muscles and the sensed adjustment signals are supplied to a signal processing unit which provides a control signal to a lens system with adjustable focal length for adjusting the focal length thereof depending on the focal adjustment signals of the ciliary eye muscles.

The invention resides in a sensor system for determining the controlsignals activating the ciliary muscles of an eye via a contact elementwhich is disposable on the cornea around the iris of an eye and consistsof an electrically nonconductive material on which sensors are arrangedin an annular array and a signal processor arranged on or in the contactelement.

The sensor system includes furthermore an evaluation system fordetermining the accommodation needs of an artificial accommodationsystem preferably of an artificial lens or an ophthalmic technicalsystem.

The human eye is a natural optical system which depicts objects on theretina by way of several light refracting boundary surfaces with sharpdefinition. When the distance of the object being observed changes, theimaging conditions of the optical system need to adapt to maintain thesharp definition of the object. In the human eye, this is accomplishedby a deformation of the lens by means of the ciliary muscle (musculusciliaris) whereby essentially the shape of the front and the rearsurfaces, that is, the curvature of the lens is changed (accommodation).

However, with increasing age, the human eye loses its capability foraccommodation, that is, the capability of the natural lens system toadapt to different distances by adjusting the curvature or focal lengthof the lens. In the healthy eye, the focal length is changed in that theabove mentioned curvature of the lens is changed by changing the radiusof curvature of the lens surfaces by activation of the ciliary muscleswhereby the degree of refraction is changed. However, with increasingage, the natural lens becomes stiffer and can no longer change itsradius of curvature sufficiently to provide for different focal lengths.This loss is compensated for with viewing aids such as glasses, theperson suffers from presbyopia.

However, even when, with increasing age, the human eye lens becomes morerigid and can no longer adjust to different viewing distances, theciliary muscle remains active. In [1] it is described that the ageaffects the ciliary muscle activity only slightly, that is, that theciliary muscle activity decreases with increasing age but neverdisappears completely. Independent thereof are the control signals forthe ciliary muscles which remain essentially unchanged with increasingage.

Another reason for the loss of the accommodation capability is thecataract. With this condition, the natural lens becomes cloudy to anextent that a person becomes blind. For the treatment of this conditionat this point, an artificial intraocular lens is implanted into therespective eye which however has a fixed focal length, but at leasttransparency is re-established. Because of its fixed curvature, anaccommodation of the eye is not possible although the control signalsare still supplied to the ciliary muscles.

In order to compensate for a missing accommodation capability of thenatural eye, various attempts to develop accommodating ophthalmictechnical systems have become known. Besides an artificial accommodationsystem which includes an implant installed, see [23], like anintraocular lens into the eye, also actively accommodating systems arebeing developed as integral parts of contact lenses or glasses; see[6-8]. Contact lenses have in comparison to implants into the lenscavity a relatively small volume and, accordingly have a smallerinstallation space for integrated active components. The arrangement ofcontact lenses on the cornea of the eye poses requirements which differfrom those of systems installed in the lens cavity and also offerdifferent possibilities for the realization of the sensor unit fordetermining the accommodation needs. With the aid of the informationregarding the accommodation needs, the active optical system integratedinto the contact lens can be adjusted to the focal length needed by apatient for viewing an object at a particular distance.

Determination of the accommodation needs of an eye is possible by adetermination of the ciliary muscle activity. The control signals of theciliary muscle can be detected via the electric activities of themuscles for example by potential measurements.

In practice, surface electrodes or muscles fine conductor electrodes incontact with, or implanted into, the muscle have been found suitable fordetermining the muscle activity. However, most known systems formeasuring the muscle activity are limited to measuring larger muscleareas.

In [3], in connection with an implantable artificial accommodationsystem, the possibility is discussed to measure The muscle potential ofthe ciliary muscle from capsule cavity and to determine theaccommodation needs in this way. It is pointed out that the measurablepotential in the capsule cavity was too low because of the largedistance of the implant from the ciliary body.

[4] discloses a testing arrangement for measuring potentials directly onthe cornea of an eye. To this end, four electrodes are disposed directlyon the cornea in the area of the iris wherein one of the electrodes hasa direct contact with the cornea. The electrodes are provided withconductors which are connected via the open eye to a further signalprocessor.

[5] discloses a contact lens with four electrodes especially for amulti-dimensional determination of the ciliary muscle activity. Theelectrodes are arranged on the inner side of a contact lens ail at thesame distance from the contact lens center point and also equally spacedfrom one another. The contacts to the electrodes are established byconductors disposed on the outside of the contact lens. Although thisarrangement was intended for the exploration of the activity of thevarious muscle fibers of the ciliary body during accommodation, noseparate detection of signals of individual fiber directions is providedfor. The arrangement and the measuring principle do not permit adetermination which of which muscle signals the measured signal iscomposed. As a result, it is for example not possible to distinguishbetween the activity of the ciliary muscles and the activity of the irismuscles. A reliable determination of the accommodation need is thereforegreatly limited.

It is the object of the present invention to provide a sensor system fordetermining the control signals of a ciliary muscle of an eye with adirectional resolution so that the signal is suitable for determiningthe accommodation needs of the eye.

SUMMARY OF THE INVENTION

In a sensor system for determining the control signal supplied to theciliary muscles of an eye for adjusting the focal length of the lens ofan eye, a contact element of an electrically non-conductive material andprovided with sensors is disposed on the cornea of the eye so that thesensors are arranged in contact with an annular area of the cornea nextto the ciliary eye muscles thereby to be able to sense the focaladjustment signals supplied to the ciliary muscles, and the sensedadjustment signals are supplied to a signal processing unit whichprovides a control signal to a lens system such as glasses or a contactlens with adjustable focal length for adjusting the focal length thereofdepending on the focal adjustment signals of the ciliary muscles.

It is important that the control signals are actively applied to theciliary muscles and these signals are detectable on the cornea of theeye; not at the capsule cavity which is more remote from the ciliarymuscles. The ciliary muscle adjoins the area around the iris.Consequently, the sensor system comprises a contact element applied tothe cornea around the iris of an eye.

If the contact element is a contact lens, not only the sensor system butalso a complete ophthalmic technical system, preferably an artificialaccommodation system including the sensor system mentioned earlier andan artificial lens with adjustable focal lengths or a lens system aredisposed in the contact lens (active contact lens). Preferably, all thecomponents required for a self-sufficient operation of the accommodationsystem are disposed on, or integrated into, the contact lens.

If the contact element is a contact ring, it extends preferably aroundthe iris without covering the iris or the pupil. The sensor systemdetects in this embodiment only the eye control signals of the ciliarymuscle, processes these signals to form a system control signal andsupplies this system control signal preferably via correspondingtransmission means (for example via electromagnetic waves or viaconductors) to an independent ophthalmic technical system such asaccommodating glasses or an implantable adjustable lens system. To thisend, the control system comprises a signal processor with transmissionmeans to a lens body or lens system whose focal length is adjustable bythe control signal, wherein the transmitted signals do not necessarilycomprise the control signal.

The ciliary muscle serves to adapt the lens in an eye to objects atdifferent distances. The ciliary muscle comprises two groups of musclefibers which are oriented differently and act independently of eachother, the so-called Müller muscle whose fibers extend annularly aroundthe lens of the eye that is tangentially to the iris, and the so-calledBrück muscle whose fibers extend meridionally, that is, radially withrespect to the axis of the lens. The Müller muscle extends around thelens and controls the radial contraction of the ciliary body. By acontraction, the zonula fibers are de-tensioned whereby the form andsurfaces of the lens and, as a result, the focal length of the lens arechanged. The Brück muscle is to change the axial position of the naturallens. The Müller muscle serves in particular for close-up accommodation,the Brück muscle is used for distance setting adjustment. An age-relateddecrease of the accommodation capability is not caused by a reducedmuscle activity but rather by a stiffening of the eye lens.

In a state of rest, that is, when not subjected to control signals, themuscle establishes a rest potential of for example about −85 mV. Duringthis state, sodium ions flow into the muscle cells and calcium ions flowout of the muscle cells. As a result, the cell potential changes for ashort period of for example about 2 ms to for example 30 mV(depolarization), which, subsequently, rapidly drops again(re-polarization) and reaches again the rest potential via a counteroscillation (hyper-polarization). This excitation occurs within a periodof about 2-4 m/s along a motorized nerve through the muscle, that is, inthe muscle fiber direction. The potential, change caused thereby can bemeasured providing an indication for the muscle activity.

An essential feature of the solution according to the invention is basedon the possibility to selectively determine the control signals of theMüller and the Brück muscles which are characterized by theirorientation around the iris. For this purpose sensors are proposed whichcomprise at least three electrodes oriented in at least one directionand arranged in series. The sensors include in each case a centerelectrode (reference electrode) and, at each side thereof, a measuringelectrode disposed adjacent and parallel to the reference electrode.While a reference potential is applied to the center electrode, the atleast two adjacent measuring electrodes detect the respective localadjacent potentials on the cornea. These sensor electrodes which arearranged preferably directly on the cornea determine in an advantageousway the electric potential differences relative to the center electrode(one measurement per electrode) selectively in the respectiveorientation. When a muscle fiber is stimulated by the application of avoltage, this voltage can be detected by potential differences presentat the two measuring electrodes only if the fiber orientation isparallel to the sensor orientation. When a measurement error for examplebecause of a displacement of the electrodes from the muscle fibers or byan orientation deviating from the fiber orientation can be detected byway of a larger deviation of the potential differences determined in asensor in a particular direction, the particular measurement value canbe eliminated by a subsequent signal processing for a control of forexample an ophthalmic technical system.

In a preferred embodiment, the sensor system comprises at least twosensors with orientations extending in tangential as well as radialdirections with respect to the iris. In this way, the signals of themuscle fibers oriented radially to the iris, that is the Brück musclesas well as the signals of the muscles oriented tangentially with regardto the iris, that is the Müller muscles, can be selectively determined.

A further improved selective determination can be achieved in that eachsensor comprises either only a tangentially or only a radially orientedsensor, that is, no sensors deviating from a predetermined orientation.Preferably, the last mentioned sensors are arranged alternately in anannular array around the iris.

The sensor system comprises furthermore a signal processor which isdisposed on the contact element. The sensors are in communication withthe signal processor via sensor conductors for transmitting data. Thesignal processor comprises preferably a signal conditioning arrangement,a signal recognition arrangement and a generator for generating acontrol signal. The signal conditioning arrangement processes the rawdata of the sensors, that is, in particular it serves the elimination ofnoise signals. It comprises, in addition to amplifier stages, inparticular signal manipulating components such as filters andrectifiers. The signal recognition arrangement receives the conditionedraw data of the sensors and supplies them to a signal evaluationarrangement. On the basis of the conditioned signals a signal generatorprovides on one hand control signals for the sensors and the subsequentsystem such a technical ophthalmologic system with adjustable lenses oran artificial accommodation system, on the other hand. The signalevaluation arrangement supplies for each sensor the activation potential(control signal) for the respective muscle strands.

The signal evaluation arrangement compares and processes the raw sensordata so as to determine an activation value of the ciliary muscle (forexample, position for near accommodation, mainly caused by the Müllermuscle fibers, zero for the resting state and negative for theactivation of the Brück muscle fibers for distant accommodation). It isan object of the signal evaluation to suppress in this way thedisturbances or noise and the isolation of the cumulative muscle fibersignals for each of the Müller and the Brück muscle fiber strands. Tothis end, the signal evaluation needs preferably also all calibrationdata which can be transmitted via a communication interface.

The present invention is concerned furthermore with the use of theabove-mentioned means for controlling (control or initiation) of anaccommodation need determination and/or a focus adjustment for theophthalmological technical system or an accommodation system as well asa method for controlling an ophthamological technical system or anaccommodation system.

The evaluation of the muscle signals of the ciliary muscle has all theadvantages of a pupil proximity reflex sensor such as the use of thebody-inherent control circuit for the natural accommodation and theintuitive use by the system carrier. Noise effects such as incidentlight do not affect the ciliary muscle which promises a substantialincrease in reliability. The relatively low complexity of the signalprocessing and evaluation of the ciliary muscle activity promises verylow energy requirements for the measuring and evaluation system.

A pupil proximity reflex sensor detects a body reaction which may alsocomprise the issue of a signal of an accommodation control circuit. Ifsuch a signal can be determined selectively, that is, separate from theother pupil reactions (for example, effects of adrenaline, caffeine,tiredness, etc. . . . ) the body-based accommodation/focusing controlcircuit may be used for the determination of the accommodation needs.Part of the accommodation control can then be taken over by the brainafter an adaption phase.

Sensors which for example determine the vergency angle between thefixation lines of the eyes can evaluate only the signals which originatemainly from the verging control circuit of the human brain. The vergencyreaction however is sometimes very much time delayed and includesover-shootings, which detrimentally affect the sensor arrangement. Inaddition, the determination of the vergency angle is affected byexternal disturbances (for example, vibrations, acceleration sensor ordistortions in the magnetic field of the earth, magnet field sensor).

An evaluation of the ciliary muscle activity is very advantageous sincethe system obtains direct access to the output signal of theaccommodation control circuit of the brain, by the evaluation of theciliary muscle activity. The accommodation needs do not need to beestimated in a complicated manner via detours but can be determineddirectly via the activation potential of the ciliary muscle. Theevaluation of the ciliary muscle consequently offers the possibility toprovide an artificial accommodation system or an artificially adjustableoptical system with a dynamics comparable to a body's normal eye lenssystem with large evaluation and calculation efforts. In an advantageousway, the human brain can learn to adjust to the artificial system.Preferably only a simple basic calibration is performed while the finecalibration is left to the learning capability of the brain

The sensor system, is basically useable for different applications.

Preferably, the sensor system is fully integrated in, or on, a contactlens. Herein, the sensors together with the signal processingarrangement as described and with an energy storage device and/orpossibly other means or sources for the input of energy are accommodatedin the edge area of the contact lens. In the center of the lens, thereis an active optical system with variable refraction capability. Therefraction capability can now be dynamically adapted to theaccommodation needs determined by the above-described sensor system.

Alternatively, the sensor system comprises a preferably contact-freetransmission means as interface to an external energy source and/or anexternal accommodating or adjustable lens system. By way of thisinterface, accommodation information can be transmitted to accommodatingglasses or an accommodating ophthalmological system. The advantage ofexternal components such as glasses as an adaptive optical elementresides in the fact that a substantially larger installation space isavailable. Such glasses comprise preferably an optical element withvariable refraction capability, a control unit for this optical element,an energy supply and also transmission means for the sensor system. Thesensor system is supplied with energy preferably by means of theglasses. In this way, the energy storage of the sensor system as suchcan be reduced to an optional energy buffer that is its size can besignificantly reduced.

Also advantageous is the use of the described sensor unit in combinationwith an active implantable accommodation system or an active intraocularlens (IOL). On one hand, the installation space for a sensor system inthe installation space-critical IOL can be saved. On the other hand, thedisadvantages of the known sensor concepts such as the convergence anglemeasurement or pupil proximity reflex for determining the accommodationneeds without utilization of the ciliary muscle signals are eliminated.The IOL includes the same elements as the accommodating glasses referredto above that is an optical element with variable refraction capability,a control unit, an energy storage device or source and transmissionmeans.

The invention and details and embodiment options thereof will becomemore readily apparent from the following description of particularembodiments with reference to the accompanying drawings which mayinclude some or all of the features mentioned earlier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b and 1 c are schematic representations of exemplaryembodiments of a sensor of the sensor system.

FIG. 2 is a partial cross-sectional view of an eye with a sensor systemapplied in the area of the pupil showing the ciliary muscle and signalsensing arrangement,

FIGS. 3 a, 3 b, 3 c, 3 d, 3 e and 3 f are schematic representations ofembodiments of the sensor system with annular electrode arrangements,and

FIG. 4 shows a diagram of a sensor circuitry including the sensors andthe sensor signal processing system.

DESCRIPTION OF PARTICULAR EMBODIMENTS

Essential elements of the sensor system are the sensors 17 with afundamental electrode arrangement as it is shown in FIGS. 1 a to 1 c inan exemplar but not limiting manner.

They comprise in each case an arrangement as shown in FIG. 1 a with anintermediate electrode 1 (reference electrode) as well as at least twomeasuring electrodes 2 which are arranged aligned at opposite sides ofthe reference electrode 1. The arrangement of the measuring electrodes 2is preferably symmetrical with regard to the intermediate electrode 1and all are preferably arranged in a single plane symmetrically aroundan axis of symmetry 3 representing the orientation 4 of the sensor.

In an embodiment of the sensor system 17 as shown for example in FIG. 1b, more than three electrodes, for example five electrodes are arrangedin a row around the axis of symmetry. This permits a free selection ofthe three adjacent electrode surface areas comprising a center electrode(reference electrode) and two adjacent aligned measuring electrodes fordetermining potential differences. This embodiment furthermore permitsthe use of more than two measuring electrodes around the referenceelectrode and also, in a particularly advantageous manner, the selectionduring operation of the number of measuring electrodes or a switch ofthe use of the electrodes as intermediate or center electrode.Preferably to selection of the three electrodes is made by a signalprocessing arrangement wherein preferably a switch-over is initiated bya deviation between potential differences determined by the sensor (forexample, upon exceeding a programmable limit). In this connection, it isadvantageous if all electrodes have a surface area which is uniform andextends symmetrically around the axis of symmetry as well as the samedistance from one another. With the arrangement as shown in FIG. 16, thesensor can remain operational, particularly upon occurrence of systemand measuring disturbances simply by the selection and switch-over ofthe control of the electrodes as reference and measuring electrodeswithout the need of a new application or replacement.

FIG. 1 c shows a sensor 17 with measuring electrodes 2 around, areference electrode 1 along two axes of symmetry arranged cross-wise.The two axes of symmetry indicate the two orientations of the sensor.

FIG. 2 shows schematically a part of the eye with applied sensor systemsincluding electrodes in a cross-sectional view. The front part of theeye 5 as shown comprises the cornea 6, the lens 7, the iris muscle 8,the pupil 9 and the ciliary muscle 10. The ciliary muscle 10 comprisesthe Müller muscle 11 and the Brück muscle 12. The representation of theeye section is divided into two halves wherein the upper half and thelower half show the eye at different accommodation states of the naturaloptical system. The deformation of the lens and the ciliary muscleconnected to the lens by zonula fibers 13 is clearly visible. The upperarea 14 represents a near view adjustment; the lower area 15 representsa far view adjustment.

On the cornea 6, a contact lens 16 is disposed as contact element andcarrier of the sensors 17. The contact element 16 has an annular area 18around the iris or respectively, the pupil which area is disposed over,and adjacent to, the ciliary muscle and on which the sensors 17 arearranged in direct contact with the cornea 6. The signal processingarrangement which is not shown in FIG. 2 comprises electronic componentsand is arranged preferably on the annular area of the contact element oris integrated into the contact element in the area above the iris. Thecentral area of the contact lens above the pupil comprises preferably anintegrated lens system (not shown in FIG. 2) for example an artificialaccommodation system with a lens system whose focal length is adjustableby the sensor system.

The electrodes are preferably arranged along the outer edge of thecontact lens and sense there the potential changes generated by themuscle activity. At the outer edge of the contact lens, the distancefrom the ciliary muscle whose signal is to be detected is only small sothat the amplitude of the ciliary muscle signal is substantially largerthan that of signals of other muscles (for example, the iris muscles)which, at this point, are more remote from the electrodes.

FIGS. 3 a-3 d disclose selected exemplary embodiments of the sensorarrangement and orientation of the sensor system. They show a front viewof the contact lens 16 wherein the eye 5 is shown schematically in thearea thereof between the upper eye lid 22 and the lower eye lid 23.

A particularly preferred embodiment as shown in FIG. 3 a comprises, inaddition to the at least four sensors disposed in a radial array 19 withregard to the central pupil area 21, at least four sensors in atangential array 20 which arrays are preferentially arranged alternatelyin the annular area 18 and concentrically with respect to, and around,the iris. The Müller muscle is an annular muscle whose control signalcan be detected at any point of the annular area in a sufficientlysecure way. The Brück muscle on the other hand extends radially withrespect to the iris. A muscle fiber of this muscle can be detected onlyby a sensor disposed directly above that muscle, so that the controlsignal for this muscle can be detected only at a particular location ofthe annular area. In addition, the Müller muscles are arranged only atthe inside of the ciliary body, whereas the Brück muscles are disposedfurther to the outside of the ciliary body. As a result of the positionof the Müller muscles at the inner edge of the ciliary body the distanceof the Müller muscles from the sensor electrodes is greater than that ofthe Brück muscles. In particular for increasing thesignal-noise-distance of the tangential electrodes, it is advantageousto arrange specifically the sensors with the tangential array in alarger number redundantly distributed over the annular area. Theembodiment represents an exemplary sensor system, wherein the sensorscomprise electrodes arranged in at least two orientations which aretangentially as well as radially oriented with respect to the iris. Byproviding several measuring locations, the signal-to-noise ratio (SNR)can be noticeably increased.

A combination of radially and tangent tally oriented electrodes resultsin a cross-shaped arrangement of electrodes of the sensors (see FIG. 1c). Preferably, in a particular embodiment at least three sensors arearranged in the annular area around the iris (FIG. 3 b).

FIG. 3 c shows another exemplary embodiment with a sensor arrangement 17including at least three, preferably exactly three, electrode rings 24which are arranged in the annular area concentrically with respect tothe iris and preferably parallel to one another. An intermediateelectrode ring serves as ground (reference potential). The electroderings are in a preferred embodiment in the form of uninterrupted rings.The array orientation of these sensors is radial with respect to thecentral pupil area 21 that is, with regard to the pupil and the iris.This sensor detects Brück muscle fiber control signals in every angulararea of the whole annulus and is particularly advantageous if individualBrück muscles are already damaged by sickness, infarcts, or paralysis.For determining the control signals, it is sufficient if a singlehealthy Brück muscle is covered by the electrode.

In a further exemplary embodiment as shown in FIG. 3 d, the annularelectrodes are divided into circular sections 25 which, in each case,cover an angular section around the iris. This facilitates a selectivedetermination of the Brück muscle signals for each annular section andconsequently the recognition and surveillance for example of changingpathological conditions such as sickness or health condition patterns inthe respective angular sections, all angular sections being covered by asignal summation. The sensor system may optionally be combined with asensor system including tangential arrays of sensors which however wouldbe provided on a separate second annular area. By comparativemeasurements of adjacent sensor, additionally differences in the controlthe Brück muscles or also a displacement of the contact elements on theeye are detectable.

A particular embodiment in this regard proposes to provide a preferablyannularly extending ring of electrodes with a plurality of individualelectrodes 26 with tangential axis of symmetry 3 and orientation (FIG. 3c). Preferably, all electrode areas are in wired communication with thesignal processing arrangement. In this embodiment, any three adjacentelectrodes can be chosen and switched to form a sensor group as desiredwithout changing the arrangement that is solely by individuallycontrolling the electrode areas via the signal processing arrangement.In a particular variant at least three electrode groups are to beactivated concurrently which electrode groups are preferably arranged atthe same distance from one another evenly distributed over thecircumference of the ring of electrodes. In this way, the controlsignals of the Müller muscles are determined at three locations whereinthe values after optional elimination of erroneous measurements arepreferably averaged. The occurrence of erroneous measurements preferablycauses the signal processing arrangement to select a new electrode groupat another location, that is, a displacement of the sensors on theMüller muscles.

In another embodiment, the annular area is divided into two or severalpartial ring areas, wherein each annular area (see FIG. 3 f) ispreferably, but not necessarily, equipped with sensors of only oneorientation. As shown in the exemplary embodiment of FIG. 3 f, in theinner annular sensor area 27, an electrode ring with a multitude ofindividual electrodes is arranged along a circle of symmetry (see FIG. 3c) for determining the Müller muscle activation signals and also anouter electrode ring 28 with annular electrodes for determining theBrück muscle activation signals is provided (see FIG. 3 c or 3 d).

Basically, the electrodes are arranged with their axes of symmetryextending preferably radially or tangentially. By the radially orientedelectrodes mainly actuation signals are detected which result from theradially extending muscle fibers (Brück muscle). It can be expected thatin the radial signal also part of the iris activity is included. Thetangential arrangement of the electrodes however results mainly in thedetection of the signals of the tangentially extending muscle fibers(Müller muscles) of the ciliary body. In the process, the influence ofthe iris muscle signals is much reduced. For smoothening the referencepotential all reference electrodes of the various measuring locationsare interconnected. It is therefore advantageous that the radialelectrode arrays are arranged at the outer partial annular area and thetangentially oriented arrays of electrodes are arranged preferably onthe inner partial annular electrode area. This arrangement also meetsthe anatomy of the eye, since the Müller muscles are—like the tangentialelectrodes—arranged further to the inside and the Brück muscles as wellas the radial electrodes are arranged further to the outside.

The sensor system 40 comprises furthermore a signal processingarrangement 39 including evaluation electronics integrated preferablyalso on the contact lens. The signal processing arrangement includes asignal conditioning unit 29 and an evaluation unit 30 with signalrecognition and a generator for providing a control signal 31. Hot shownis an energy source for the sensor system such as a capacitive energybuffer which is charged by movements of the system in the earth magneticfield, by inertia generators or eye lid movement generators.Alternatively, a contact-free transmission of the required energy fromwithout is possible for example via electromagnetic transmission means.Furthermore, solar cells may be used which convert the ambient lightinto electric energy or bio-fuel cells may be used which convert thechemical energy of the glucose of tear liquid into electric energy.

The evaluation electronics is to process the potential difference of lowamplitude between the electrodes in such a way that the accommodationcan be calculated. The measuring electrodes 2 of the sensors disposedadjacent the intermediate electrode 1 (reference potential for examplebased on ground) are connected to the signal conditioning unit 29 viaelectric conductors, preferably conductor strips, and supply themeasurement signal in the signal conditioning unit 29 first to an ESDprotection circuit 32. In this way, during common handling of thecontact lens (insertion, removal, cleaning) by the user, damage to theelectronics by electrostatic discharges are prevented. An ESD protectionarrangement protects the evaluation unit in particular during handlingby the system carrier during insertion, removal and cleaning of thesystems from excessive voltages. Then a one or multi-stage amplifiercircuit 33 follows in order to increase the amplitude of the signal.With a bi- or multi-polar configuration it is possible to suppress inphase interference voltages by a differential stage, which is preferablyformed by an instrument amplifier. Subsequently, the signal is filteredin filter 34. Disturbances and high frequency noise are suppressedpreferably in several filter stages followed by a rectifier circuit 35in which the AC signal is converted to a DC signal which is proportionalto the muscle activity. In order to be able to utilize for the detectionthe positive as well as the negative signal components, the use of afull wave rectifier is preferred. The processed rectified measuringsignal is transmitted to the evaluation unit.

The preferably two voltage detected in a sensor are optionally averagedor weighted in the evaluation unit for example by a substractor and/orfilter which processes the signals of certain electrodes which havealready been processed. For example, in particular, measuring signals inthe area near another adjacent muscle whose signals are not to bedetermined, are still influenced by the signals of the adjacent muscle.This interference influence can be recognized by a comparison ofredundant measurement signals (generally two) which are determined byseveral electrodes of a sensor and eliminated in the evaluation unit. Inthis way, also an improved separation of tangential and radial musclesignals can be achieved and for example the iris muscle signal (radial)in the tangential ciliary muscle signal can be suppressed.

The evaluation unit 30 determines from the height of the processedrectified measuring signal relative to the reference potential theaccommodation need and generates the control signal 31. In anarrangement with several measurement locations, the measuring signalsare preferably additionally averaged or weighted in order to reduce theeffects of extraneous undesirable muscle signals (for example, irismuscle signals) on the evaluation.

The control signal 31 is used for the setting of the focal length of anadjustable lens system and is transmitted to the lens system bytransmission means (conductors or contact-free via electromagneticwaves). Alternatively, the above-mentioned processed and rectifiedmeasuring signal is supplied via the above-mentioned transmission meansin a contact-free manner for example to a central evaluation unit forboth eyes.

Optionally an offset correction or calibration may foe performed. Tothis end, user-specific calibration data 38 are transmitted via acommunication interface 36 to an external computer 37 to the evaluationunit 30. As a result, the system can be rapidly adapted to an individualuser in an optimal manner.

Literature:

-   [1] Strenk, B. et al., Age-related changes in human ciliary muscle    and lens: A magnetic resonance imaging study: Investigative    Opthalmology and Visual Sci. 40 (1999, 6 page 1162-1169).-   [2] SP 1 919 360 B1-   [3] Klink S: Neues System zur Erfassung des Akkommodationsbedarfs im    menschlichen Ange, Schriftenreihe des Instituts für angewandte    Informatik/Automationstechnik der Universität Karlsruhe (TH),    edition 23 Universitätsverlag Karlsruhe, 2008, ISBN    978-3-86644-300-6.-   [4] U.S. Pat. No. 4,386,831-   [5] RU 2 281 020 C1-   [6] U.S. Pat. No. 7,404,636 B2-   [7] U.S. Pat. No. 6,851,805 B2-   [8] DE 10 2005 038 542 A1

Listing of Reference Numerals: 1 Intermediate sensor electrode 2Measuring electrode 3 Axis of Symmetry 4 Orientation 5 Eye 6 Cornea 7Lens 8 Iris muscle 9 Pupil 10 Ciliary muscle 11 Muller muscle 12 Bruckmuscle 13 Zenular lens 14 Upper area 15 Lower area 16 Contact lens 17Sensor 18 Annular area 19 Sensor with radial array 20 Sensor withtangential array 21 Pupil area 22 Upper eye lid 23 Lower eye lid 24Electrode rings 25 Circular section 26 Individual electrode 27 Innercircular sectionarea 28 Outer circular section area 29 Signalconditioning 30 Evaluation unit 31 Control signal 32 ESD-protectioncircuit 33 Amplifier circuit 34 Filter 35 Rectifier circuit 36Communication interface 37 Computer 38 Calibration data 39 Signalprocessing arrangement 40 Sensor system

What is claimed is:
 1. A sensor system for determining control signalsof a ciliary muscle of an eye having a cornea, a lens a pupil, an iris,ciliary muscles, comprising Müller muscles, and Brück muscles andzenular fibers, the sensor system comprising: a) a contact elementconsisting of an electrically non-conductive material for disposition onthe cornea in contact with the area of the eye around the iris thereof,b) a sensor system with at least one sensor applied to the contactelement in an annular array around the iris, and c) a signal processingarrangement disposed on, or in, the contact element, d) each sensorcomprising at least three electrodes oriented in the same direction andarranged in a row, e) the orientations comprising at least oneorientation extending in a radial direction with respect to the iris andf) each sensor having an intermediate electrode which forms a referencepotential and two electrodes which are disposed in the orientationdirection directly adjacent to, and at opposite sides of, theintermediate electrode and which determines an eye body potential withrespect to the reference potential.
 2. The sensor system according toclaim 1, wherein the at least one sensor is arranged on an annularsurface area of the contact element around the iris.
 3. The sensorsystem according to claim 2, wherein at least two sensors are providedwhich have orientations in tangential as well as radial directions withrespect to the iris.
 4. The sensor system according to claim 3, whereineach sensor has either only a tangential or a radial orientation withrespect to the iris and the sensors are arranged on the annular surfacearea with alternate orientations.
 5. The sensor system according toclaim 1, wherein the sensor comprise at least four measuring electrodesarranged around a center electrode in tangential and also in radialorientations with respect to the iris.
 6. The sensor system according toclaim 2, wherein a sensor comprises as electrodes three electrode ringsor ring sections arranged on the annular surface area concentricallywith respect to the iris.
 7. The sensor system according to claim 1,wherein at least four sensors with tangential orientation are provided.8. The sensor system according to claim 1, wherein the contact elementis a contact lens.
 9. The sensor system according to claim 1, whereinthe signal processing arrangement comprises a signal conditioning unitand a signal recognition unit with a generator for generating a controlsignal.
 10. The sensor system according to claim 9, wherein the systemincludes a lens system or lens with an adjustable focal length and thesignal processing arrangement includes transmission means fortransmitting the control signal to the lens system or lens for adjustingthe focal length thereof depending on the control signal.